We propose a single-blind, placebo-controlled trial of melatonin to investigate its potential to entrain (synchronize) the sleep-wake cycle of totally blind people who manifest free-running circadian rhythms. In this study, melatonin will be given by mouth for up to 8 weeks in free-running blind people in an attempt to entrain their rhythms to a 24-hour day. The timing of exogenous melatonin administration will be anchored to the timing of endogenous melatonin production.